The foundations of risk for many psychiatric disorders, including those with adult onset, are increasingly understood as arising from anomalies of neurodevelopment. In this longitudinal study (with participants returning at approximately two-year intervals) we combine brain imaging information with extensive behavioral and neuropsychological testing as well as genetic data to explore the relationship between genes, brain, and behavior in typical and atypical development. Understanding the typical path of brain development is imperative to assess whether illness are associated with deviations from that path. To this end we have acquired the worlds largest data set of well-characterized longitudinal pediatric brain MRI scans (N = 1000). This data serves as a resource for many neuroimaging projects throughout the world and has led to key insights into the biology of adolescent emotion, cognition, and behavior. To assess nature/nurture questions we are studying brain development in mono and dizygotic twins. The study of subjects with variations in the number of X and Y chromosomes (i.e. XXY, XXX, XYY, XXXXY) and subjects with hormone anomalies (i.e. Cushings disease, Congenital Adrenal Hyperplasia, Familial Precocious Puberty) allow us to discern the relative contributions of hormones and chromosomes to male/female differences in the brain. Clinical populations investigated include the largest imaging studies of ADHD and Childhood-Onset Schizophrenia. Seminal contributions to the literature have been produced in each of these areas.